The invention provides a preparation method of a low temperature poly-silicon thin film, a preparation method of a low temperature poly-silicon thin film transistor, and a laser crystallization apparatus, and belongs to the technical field of display. The preparation method of a low temperature poly-silicon thin film of the invention comprises: forming an amorphous silicon thin film on a transparent substrate; and performing laser annealing on said amorphous silicon thin film from a side of said amorphous silicon thin film departing from said substrate, and performing laser irradiation from a side of said substrate departing from said amorphous silicon thin film, to form a low temperature poly-silicon thin film. The preparation method of a low temperature poly-silicon thin film of the invention may not only perform laser annealing on an amorphous silicon thin film form a side of the amorphous silicon thin film departing from the substrate, but also perform laser irradiation from a side of the substrate departing from the amorphous silicon thin film, and the temperature of the amorphous silicon thin film can be retained by performing laser irradiation from a side of the substrate departing from the amorphous silicon thin film. In this way, the crystallization period of poly-silicon may be elongated, and it is possible to obtain crystal grains with larger sizes, to increase carrier mobility, and to reduce drain current.